The present disclosure relates to subject matter contained in priority Japanese Patent Application No. 2000-044101, filed on Feb. 22, 2000, the contents of which is herein expressly incorporated by reference in its entirety.
1. Field of the Invention
The present invention relates to a method of inspecting sealing property of battery.
2. Description of Related Art
FIG. 2 illustrates a conventional battery sealing inspection method for verifying the sealing properties of a sealed battery case. The battery case 21 is closed with a sealing plate, in which a hole 22 is formed for mounting a safety vent or the like. Compressed gas is introduced from a high-pressure gas source 23 via a valve 24 into the battery case 21, and the pressure inside the battery case 21 is measured by a pressure gauge 25. When the pressure inside the battery case 21 has reached a predetermined value, the valve 24 is closed, and pressure change thereafter inside the battery case 21 is measured by the pressure gauge 25. If a fall in pressure is observed, then the battery is identified to be a defective battery in which gas is leaking out from the battery case.
Another prior art battery sealing inspection method as disclosed in Japanese Laid-open Patent Application No. 4-25738 includes introducing of compressed hydrogen gas into a battery case, and detecting the hydrogen gas leaking out from the battery case by collector plates and a semiconductor gas sensor.
In the inspection method illustrated in FIG. 2, the amount of gas leaking from the battery case 21, if any, is fairly small relative to the volume of the battery case 21, and hence the pressure drop inside the battery case 21 due to gas leakage is very small. Therefore, detection accuracy is relatively low, because detection of gas leakage is possible only when there is a hole or a gap of more than 100 xcexcm. In order to ensure accurate detection of gas leakage with this method, it takes at least 5 to 10 minutes per each battery, resulting in extremely poor efficiency. Moreover, since the compressed air is introduced into the battery case through the hole 22 for mounting a safety vent or the like prior to the actual mounting of such parts, it was necessary to inspect the sealing properties of the battery after the safety vent has been mounted on the battery case by welding. Thus the method involves a further leakage test with respect to the welds.
In the method disclosed in Japanese Laid-open Patent Application No. 4-25738, since there is no assurance that the leaked gas will always be collected accurately by the collector plates, there are variations in detection accuracy. Also, similarly to the former method, this method involves a further inspection of sealing properties of the battery case with respect to the portion through which compressed air is introduced into the battery case.
In view of the foregoing problems of the prior art, an object of the present invention is to provide a battery sealing inspection method whereby gas leakage from any location on a battery case is detected with a high degree of accuracy, good efficiency, and high reliability.
In a method for inspecting sealing properties of a battery according to the present invention, the battery is made to undergo charging and discharging before being placed within a sealed vessel. The sealed vessel is then evacuated, and a certain low pressure inside thereof is maintained for a predetermined period of time. The density of a gas within the sealed vessel, the gas being a gas generated within the battery, is measured, based on which it is determined whether there is a gas leak from the battery, by comparing the measured gas density with a preliminarily obtained reference value.
The characteristic feature of the invention is that the battery is charged and discharged prior to inspection so as to raise the internal pressure of the battery. Moreover, the sealed vessel in which the battery is placed is evacuated so as to make the internal pressure of the battery even higher relative to its ambient pressure. Since the battery is housed within the sealed vessel, a gas leak, even in a slightest amount, from any location of the battery is detected by the measurement of gas density within the sealed vessel. Thus the inspection method ensures detection of a hole or a crack as small as about 10 xcexcm with good efficiency and high reliability.
The inspection should preferably be performed immediately after the battery has undergone initial charging and discharging, where the internal pressure of the battery is particularly high.
In another embodiment of the invention, a battery which has been filled with electrolyte and has been sealed is placed within a sealed vessel, and is heated to a predetermined temperature. The sealed vessel is then evacuated, and a certain low pressure inside thereof is maintained for a predetermined period of time. The density of a gas within the sealed vessel, the gas being a gas generated within the battery, is measured, based on which it is determined whether there is a gas leak from the battery, by comparing the measured gas density with a preliminarily obtained reference value.
In this embodiment, the battery is heated instead of subjected to charging and discharging in order to raise the internal pressure thereof. Therefore the inspection is performed with good efficiency and high reliability similarly to the above described embodiment. This embodiment is also effective for the inspection of batteries that have been stored for a long period of time after initial charging and discharging.
The battery should preferably be heated to a temperature between 45xc2x0 C. and 80xc2x0 C., and more preferably to 65xc2x0 C. plus or minus 5xc2x0 C. This temperature range enables the battery internal pressure to be a level optimal for accurate detection of gas leakage, while preventing degradation of other members which will not withstand high heat such as separators.
The gas generated within the battery is hydrogen, and the reference value is obtained by measuring hydrogen density in an ambient atmosphere prior to evacuation of the sealed vessel. In this way, the inspection is performed without being affected by the initial hydrogen density of ambient atmosphere, and gas leakage is accurately detected.
While novel features of the invention are set forth in the preceding, the invention, both as to organization and content, can be further understood and appreciated, along with other objects and features thereof, from the following detailed description and examples when taken in conjunction with the attached drawings.